Year	Percent
1991	38.575
1992	37.499
1993	35.764
1994	33.878
1995	33.718
1996	32.264
1997	30.483
1998	29.916
1999	27.767
2000	28.321
2001	28.943
2002	28.662
2003	26.085
2004	25.393
2005	25.382
2006	23.671
2007	22.995
2008	22.703
2009	21.716
2010	20.543
2011	18.34
2012	18.253
2013	18.315
2014	17.881
2015	18.244
2016	19.163
2017	18.551
2018	17.71
2019	16.998
2020	16.502
2021	16.185
2022	15.864